The present invention relates to a series of new macrolide compounds which are chemically related to certain known classes of macrolides including those known as the milbemycins and the avermectins. These compounds have valuable acaricidal, insecticidal and anthelmintic activities. The invention also provides methods of preparing these compounds and compositions and methods for using them.
There are several classes of known compounds with a structure based on a 16-membered macrolide ring, which compounds are obtained by fermentation of various microorganisms or are obtained semi-synthetically by chemical derivatization of such natural fermentation products, and which exhibit acaricidal, insecticidal, anthelmintic and antiparasitic activities. The milbemycins and avermectins are examples of two such classes of known compounds, but various others also exist and are identified in the art by different names or code numbers. The names for these various macrolide compounds have generally been taken from the names or code numbers of the microorganisms which produce the naturally occurring members of each class, and these names have then been extended to cover the chemical derivatives of the same class, with the result that there has been no standardized systematic nomenclature for such compounds generally.
In order to avoid confusion, a standardized system of nomenclature will be used herein, which follows the normal rules for naming derivatives of organic compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC), Organic Chemistry Division, Commission on Nomenclature of Organic Chemistry, and which is based primarily on the hypothetical parent compound hereby defined as "milbemycin" and represented by the formula (A): ##STR2## For the avoidance of doubt, formula (A) also shows the numbering of positions of the macrolide ring system applied to those positions most relevant to the compounds of the present invention and of the prior art.
The naturally produced milbemycins are a series of macrolide compounds known to have anthelmintic, acaricidal and insecticidal activities. Milbemycin D was disclosed in U.S. Pat. No. 4,346,171, where it was referred to as "Compound B-41D", and milbemycins A.sub.3 and A.sub.4 were disclosed in U.S. Pat. No. 3,950,360. These compounds may be represented by the above formula (A) in which there is a hydrogen atom at position 13 and position 25 is substituted with a methyl group, an ethyl group or an isopropyl group, these compounds being designated as milbemycin A.sub.3, milbemycin A.sub.4 and milbemycin D, respectively. The milbemycin analog having a hydrogen atom at position 13 and substituted at position 25 with a sec-butyl group was disclosed in U.S. Pat. No. 4,173,571, where it was known as "13-deoxy-22,23-dihydroavermectin B.sub.1a aglycone". Certain of the compounds of the present invention are named as derivatives of this and related compounds, the numbering system being as shown above on formula (A).
Subsequently, various derivatives of the original milbemycins and avermectins have been prepared and their activities investigated. For example, 5-esterified milbemycins have been disclosed in U.S. Pat. Nos. 4,201,861, 4,206,205, 4,173,571, 4,171,314, 4,203,976, 4,289,760, 4,457,920, 4,579,864 and 4,547,491, in European Patent Publications Nos. 8184, 102,721, 115,930, 180,539 and 184,989 and in Japanese Patent Applications Kokai (i.e. as laid open to public inspection) No. 57-120589 and 59-16894.
13-Hydroxy-5-ketomilbemycin derivatives have been disclosed in U.S. Pat. No. 4,423,209. Milbemycin 5-oxime derivatives were disclosed in U.S. Pat. No. 4,547,520 and in European Patent Publication No. 203 832.
Milbemycins having an ether linkage at the 13 position are of particular relevance to the present invention and the lower alkyl, phenyl and benzyl ethers are described in general terms in U.S. Pat. No. 4,696,945, but only the methyl and ethyl ethers are specifically described in the Examples. Certain other milbemycin derivatives having a 13-ether group are disclosed in European Patent Publication No. 357 460.
Like the milbemycins, the avermectins are based upon the same 16-membered ring macrolide compound. The avermectins are disclosed, for example in J. Antimicrob. Agents Chemother., 15(3), 361-367 (1979). These compounds may be represented by the above formula (A) but with a carbon-carbon double bond at positions 22 and 23, and having position 13 substituted with a 4'-(.alpha.-L-oleandrosyl)-.alpha.-L-oleandrosyloxy group. Position 25 may be substituted with an isopropyl group or a sec-butyl group, these compounds being designated as avermectin B.sub.1b and avermectin B.sub.1a, respectively. 22,23-Dihydroavermectins B.sub.1a and B.sub.1b may be obtained by reduction of the double bond between the 22 and 23 positions and are disclosed in U.S. Pat. No. 4,199,569. The aglycone derivatives of the avermectins, which are milbemycin analogs, have sometimes been referred to in the literature as C-076 compounds, and various derivatives of these are known. For example, U.S. Pat. No. 4,201,861 discloses such derivatives substituted with a lower alkanoyl group at position 13.
European Patent Publication No. 170 006 discloses a family of bioactive compounds produced by fermentation, identified collectively by the code number LL-F28249. Some of these have a 16-membered macrolide structure corresponding to the above formula (A), substituted with a hydroxy group at position 23 and with a 1-methyl-1-propenyl, 1-methyl-1-butenyl or 1,3-dimethyl-1-butenyl group at position 25. In these compounds, the hydroxy group at position 5 may also be replaced by a methoxy group.
British Patent Publication No. 2,176,182 discloses another group of macrolide antibiotics corresponding to the above formula (A) with a hydroxy or substituted hydroxy group at position 5, a hydroxy, substituted hydroxy or keto group at position 23, and an .alpha.-branched alkenyl group at position 25.
The various classes of milbemycin-related macrolide compounds described above are all disclosed as having one or more types of activity as antibiotic, anthelmintic, ectoparasiticidal, acaricidal or other pesticidal agents. However, there is still a continuing need to provide such agents with improved activity against one or more classes of pests.
It has now been discovered that the activity of such milbemycin-related derivatives can be improved by appropriately selecting the combination of substituents on the macrolide ring system, especially the substituents at position 13. In particular, it has now been found that the activity of the compounds can be improved upon by appropriate selection of certain highly specific ether groups at the 13 position, as specified below.